This proposal requests addition of S-band (3.5 GHz) and Q-band (35 GHz) capability to the X-band (9.5 GHz) pulsed Electron Paramagnetic Resonance (EPR) spectrometer system (ELEXSYS, E-580) currently available on campus. This will provide a strong and diverse biomedical research community on this campus, and external users from academia and industry, with a versatile, state-of-the art tool in EPR spectroscopy for structural biology. The proposed enhancement is particularly critical for the successful development of research projects performed by six named NIH-funded major-user groups. The instrument will be sited in UIUC EPR Research facility space within the School of Molecular and Cellular Biology (SMCB), and will be operated and managed under the SMCB administrative umbrella. The ELEXSYS E- 580 was previously under management by the Illinois EPR Research Center, and that unit was reorganized within SMCB subsequent to the reorganization of the life sciences on campus. PUBLIC HEALTH RELEVANCE: A main focus of modern molecular biology is on understanding how structure at the molecular level defines mechanism and function. This interface is of critical importance in understanding catalysis, effector binding, drug design, etc., indeed the whole underpinning of the medical sciences by molecular biology. Surveys suggest that >30% of the protein-encoding genome encodes either redox proteins, or proteins that include metal binding sites suitable for probing by EPR. Pulsed EPR approaches follow the relaxation kinetics of paramagnetic centers and the modulation by interaction with nuclear magnetic centers in the protein and solvent. By Fourier transformation, the frequencies of the nuclear magnets, and hence their atomic identities, distance and angles, can be measured. The distance dependence of the interaction selects that volume most closely associated with the catalytic domain. Redox enzymes generate paramagnetic centers naturally, while, for example, nucleotide binding enzymes where the Mg2+chelate is the substrate can be probed by replacing the ion by paramagnetic substituents. For these paramagnetic systems, pulsed EPR is an ideal approach for investigation of the protein environment immediately adjacent to the functional center, and is therefore an invaluable tool in the advancement of medical knowledge.